Diagnosis Colony either with erect, branched or unbranched hydrocaulus, monosiphonic or polysiphonic or stolonal (Ophinella); issued from a creeping hydrorhiza; hydrocladia alternate, arising in polysiphonic hydrocauli from a single dominant axial tube; hydrothecae small, occurring only on hydrocladia, with or without marginal cusps, with or without an abcauline intrathecal septum, adnate or not; nematophores with nematothecae often rudimentary or occurring as naked sarcostyles; when present, nematothecae simple, typically one-chambered although two-chambered in some species, not fused to hydrothecae; paired lateral nematophores and nematothecae absent; gonophores as fixed sporosacs; gonotheca solitary, lacking nematothecae, on stem or hydrocladia, exceptionally on hydrorhiza (Pycnotheca). [details]